Explosive



Patented Aug. 13, 1940 I UNITED EXPLOSIVE of Delaware No Drawing.Application November 18, 1936, Serial No. 111,372

12 Claims.

This invention relates generally to explosives and particularly toblasting explosives of the type containing carbonaceous material as wellas to the process of preparing such explosives and the ingredientsthereof.

Blasting explosives, such as the low density dynamites of thepermissible type generally comprise a liquid explosive, such asnitroglycerine, inorganic explosive salts, such as ammonium nitrate, anda bulky carbonaceous filler. Permissible dynamites are designedparticularly for use in mining coal, and their composition is such as tominimize the formation of toxic concentrations of carbon monoxide and toavoid danger of fire and explosion in the mine clue to dust.

The density of permissible dynamites can be decreased by increasing theproportion of the bulky carbonaceous ingredient up to about 20%, whichconstitutes the upper limit since higher percentages cause excessiveconcentrations of carbon monoxide in the explosion gases. The maximumproportion of filler is further limited, for a given percentage ofnitroglycerine in the explosive, to an amount which permits satisfactorysensitivity to detonation, i. e., the explosion of a cartridge mustinitiate the explosion of a similar cartridge placed some minimumdistance away, for example over a gap of three inches between the endsoftwo cartridges or ten inches between the open ends of two halfcartridges. In general,

the lower the nitroglycerine absorptivity of a given filler, the lesswill be the effect of the filler in decreasing the sensitivity ofdynamites in which it is used. Loss in sensitivity may be corrected byincreasing the percentage of nitroglycerine, but this involves thedisadvantages of increased cost of the explosive and higher flametemperature, density, and rate of detonation.

Heretofore various materials have been eml ployed as the carbonaceousfiller in such low density dynamites. A great variety of materials ofvegetable origin, such as plant stalks, moss, various kinds of woodflour, or sawdust, have been employed. In general, however, suchmaterials are too highly absorbent of nitroglycerine to permit their usein the manufacture of permissible dynamites of very low density as, forexample, dynamite of the type such that more than about five hundred 1%inch x 8 inch cartridges may be obtained per one hundred pounds ofdynamite. While various methods have been heretofore suggested fortreating such materials in'order to reduce their abscrptivity as, forexample, by impregnating them with resin, starch or inorganic salts,such treatments frequently increase the density of the filler and in anyevent are disadvantageous because of the additional manufacturing costand difficulty of obtaining a uniformly treated product.

The object of the present invention, generally 5 stated, is to provide alow density dynamite having a carbonaceous filler ofplant stalk materialwhose absorptivity for nitroglycerine is low.

Another object of the present invention is to provide an improvedcarbonaceous filler for low density dynamite.

A further object of the present invention is to provide a process oftreating low density plant stalk material whereby the low density ismaintained without rendering the material highly absorptive towardnitroglycerine.

A more specific object of the present invention is to provide a processof preparing carbonaceous filler material of the plant stalk typewhereby the cell walls of the stalk are maintained substantia-lly intactand the nitroglycerine absorptivity minimized.

Other objects will become apparent to those skilled in the art when thefollowing description isread.

In accordance with the present invention an explosive composition of thedynamite type containing a carbonaceous filler is prepared with acarbonaceous filler material which, while being substantially void onits interior and thus having a low density, is composed of particles,the surfaces of which are substantially continuous and hence thea'bsorptivity toward nitroglycerine is minimized, such. nitroglycerineas attaches itself to the filler being for the most part by adsorption.In accordance with one feature of the present invention the carbonaceousfiller material may be prepared from low density plant stalks in suchmanner that during the process of treatment including subdivision, thecell walls of the stalk are maintained substantially intact and free ofrupture or puncture insofar as possible, save along the lines ofsubdivision. Such preservation of the cell walls structure results in afiller material which, while of low density, is so because of 5 internalvoids having no channel of communication. with the surface of theparticle. Hence, upon the exposure of the filler material tonitroglycerine, the nitroglycerine cannot penetrate to the interior andoccupy the voids, but, on the contrary, must confine itself to thesurfaces of the particles of filler material.

Such preservation of cell wall structure may be accomplished bysubdividing the material by a process of cutting with knives or shearingas distinguished from the usual process of comminution which involves agrinding, shredding or rasping action. Particularly beneficial resultsare obtained if the material is cut while containing a substantialpercentage of moisture as, for instance, a moisture content sufiicientto saturate the cell walls of the material. In the Case of most lowdensity annual plant stalks a moisture content of 25% to 50% (on theweight of the oven dry material) is sufficient to saturate the cellwalls. The process of preparingfiller material in accordance with thepresent invention is particularly applicable to annual plant stalks ofthe type having a substantial pith content such, for instance, as thestalks of broom corn, sugar cane, sorghum cane, corn and sunflower.

In accordance with the present invention, after the plant stalk materialhas been subdivided in the manner, just described, the filler materialmay be processed by further wetting as, forjin'sta'nce,

with water or with steam followed by drying. This treatment results in aslight expansion of the particles as well as a stiffening thereof, thelatter result being accomplished apparentlydby the partial hydrolysis ofthe hemi-cellulose compounds of the cell walls. After such hydrolysis ofthe hemicellulose comp nents and upon drying of the material,the-hydrolytic products are left, upon evaporation of the water, at ornear the exterior surface "of the particles with the result that thecell walls thereafter are impregnated, stiffened and strengthenedthereby. The stiffness and strengthening of the filler material is ofparticular importance in view of the fact that dynamite cartridges areloaded under pressure, and, ifthe filler material does not possesssufficient stiffness of strength to withstand the pressure ofloading, itis apparent that the particles of filler collapse with consequentincrease in the density of the explosives.

A convenient device for use in subedividing the plant stalk material inaccordance with the pres-.

ent invention in order to effect subdivision without substantiallyrupturing or puncturing the cell walls except along the lines ofsubdivision is a device known as a rotary'knife cutter. This apparatusconsists of a rotor'fitted with knives, rotating within a cylindricalcasing provided with stationary knives and having perforated sides. Thedesired particle size is obtained by adjusting the speed of rotation,the clearance between the stationary and rotating knives, and the sizeof the perforations in the screen enclosing the cutting chamber. Thestalks are therefore severed into particles by clean cuts so that thesurfaces or edges of the particles are smooth and even andso that theinterior walls of the particles remain substantially intact. Inoperation, particles which have been cut to the desired size areimmediately discharged through the screen, particularly if suction isapplied around the cutting chamber accordingto the usual practice, andthe desired subdivision is thus obtained with minimum crushing andlaceration of the cell walls, and is accompanied by the formation ofonly a small percentage of fines. In contrast to material which has beencomminuted by other means, the rotary knife cutter product ischaracterized by substantial uniformity in the shape of. the particlesand by the absence of slivers.

In comparative experiments in the comminu tion of broom corn stalks forexample, the following yields of material passing through an 8 mesh andretained on .a 30 mesh screen were obtained:-49% by means of ahammer-mill, the

overs having been re-milled four times; 43% by means'of a rasping wheel;and 88% by a single pass through a rotary knife cutter. The percentagesof fines were respectively 23 25%, and 12% and of overs 28%, 32%, andnone for the rotary knife cutter. The product obtained with the ro--tary knife cutter was free of slivers as contrasted with the'other twoand fiowed more readily. The

-'overs "obtained from the hammer milling and 1 'densityplant tissue;for example,.screened yields of corn-stalk, obtained as above, were 67%,55%

- and respectively. The following table illustrates the differences incharacteristics between .material subdivided in accordance with thepresent invention and. that subdivided by other means of comminution:

As pointed out hereinbefore, it is advantageous that the plant stalkmaterial be cut in a moistened condition. For instance, in the case ofbroom corn stalks, optimum values of density and nitroglyceriiieabsorption are obtained when the material is .cut at a moisture contentgreater than 25% of the weight of the. oven dry material. ZS-50%moisture by weight of oven dry material commends itself as this moisturecontent is sufficient to reduce the brittleness and hence inhibitstearing and puncturing of the cell walls while it is not so great thatsubstantial amounts of free water will be present, and consequentlysticking and clogging of the cutting apparatus is M th d i 5%? D 1mm?- eo 0 eng ycerme Mammal g r; Subdivision mesh sity abs0rpproduct tionPercent Broom corn 7-10 Rotary knife 88 0.133 2.90 s s. cutter.

D0 7-10 Hammer mill 49 0.122 2. 23 Do 7-10 Raspingwheel 43 0.115 4.08 vCorn stalks... 10 Rotary knife 85 0.123 2.57

cutter. Do... l0 Hammermill. 67 0.124 2.38 Do l0 Raspingwheel 55 0.1352.67

avoided. -In the case of broom corn stalks, at

Nitro- Material Percent Density glycerine H20 absorption Broom cornstalks 7 0. 133 2.00 18 080 2. 07 d! 086 1. 55 75 092 1. 7! Corn stalksl0 123 2. 57 3O 127 l. 67 75 097 l. 62

Material such as broom corn stalks which has been cut wet. ashereinbefore described, may be further improved by an after treatmentwith about an equal weight of water followed by drying at a temperaturefrom -150" C. As

Nitroglycerine absorption Percent moisture added Density As comparedwith a known carbonaceous filler material consisting of expanded flakedcereal grain, it may be pointed out that the density of such flakedcereal grain product is 0.091 while the nitroglycerine absorptivitycharacteristic is 2.83

according to the method used in determining those characteristics as setforth in the foregoing tables.

In the'foregoing tables the density values were determined by filling atared glass cylinder of known volume, 40 mm. in diameter and 250 mm.high, with the material, which was compressed during the fillingoperation at A, A, and full measure by means of a closely fitting woodenplunger carrying a 15 pound weight, and weighing.

In the foregoing tables the nitroglycerine absorptivity values weredetermined by the following method: About 25 gms. of filler are mixedwith. '75 gms. of nitroglycerine and stored for 2 hours at 100 F. withoccasional stirring. A portion of the mixture is then centrifuged in atared Gooch crucible at 600 R. P. M. for 5 minutes and the crucible andcontents weighed. The nitroglycerine is then extracted with ether andthe weight during a blank ether extraction).

As an illustrative example of the present invention the stalk of variousvarieties of broom corn (Standard, Western Dwarf, or Whisk Dwarf), thebrush of which is utilized in the manufacture of brooms, may be employedas the raw material. The stalks may be cured in the field after theharvesting of the broom and are then stored to be used as needed. Thestalks are passed through an ensilage cutter and cut to short lengths offrom a fraction of an inch to several inches. The stalk segments arethoroughly sprayed with water and allowed to stand in heaps for at leastan hour. They are then spread out in a thin layer and allowed to drainand air-dry for about 12 hours, or for a shorter time if a forced airdraft is used, until the moisture content is about 25 to 40% of theoven-dry weight of material. A rapid rate of drying is preferable sincethen the outermost layer of the speed of rotation, clearance betweenknives, and

the size of the screen perforations are adjusted so as to yield aproduct of the desired granulation, with minimum production of fines.-The material is then sprayed with an equal weight of water or mixture ofwater and steam and then dried at temperatures between 100 and 150 C.

by means of apparatus, such as a continuous plate or rotary dryer, whichserves to keep the material well stirred, loose, and substantially freefrom any crushing, to a moisture content of about 3%. The product isscreened by customary means, a yield of over 80% of particles passingthrough an 8 mesh but retained on a 30 mesh screen being obtained. Theproduct has sufiiciently low density and low absorptivity towardnitroglycerine to permit its use as the carbonaceous ingredient inpermissible dynamites providing more than 500 1% x 8 inch cartridges per100 pounds. If a product of still lower density is desired, it may beobtained by removing the heavier particles by means of air or gravityseparation after the cutting operation and applying the spraying,drying, and screening treatments as described above to the lightfraction. The fines which result at the final screening, amount to lessthan 15% of the raw material and may be utilized as the carbonaceousingredients of higher density dynamites or for other uses. 5

The preparation of the product may be conveniently carried outcontinuously in the following manner. The stalks are passed through anensilage cutter and the short lengths are treated with excess water,drained, and partially dried while being conveyed to the hopper .of arotary knife cutter, the resulting particles being discharged into acyclone collector. Thematerial is then passed through mixing apparatusof the screw conveyor type, being subjected to a fine spray of water orWet steam near the charging end, preferably adjusted to-treat theparticles with about an equal weight of water. The material is thenpassed through drying apparatus, which may be a continuous plate dryerof the type in which the material is carried from one end of a heatedmetal plate to the other by means of intermittently operating scrapers.of travel through the apparatus may be adjusted according to the platetemperature, for example one hour for a plate temperature of 130 orlonger periods for lower temperatures. After the treatment in the dryer,the particles at a moisture content of about 3 are transferred by meansof an air blast, which serves also to cool the material, to a screeningapparatus, and the product passing through an 8' mesh and retained on a30 mesh screen is stored or packed for use in low density explosives.During the steaming and drying treatments, the color of the product maybecome deepened because of partial carame1iza tion.

Another waste product of the broom industry which forms a highlysatisfactory raw material for the preparation of very low densitycarbonaceous filler consists of the handle or stem of the brush,commonly called broom chips, which are obtainable from broom factories.This material comprises one to twelve inchlengths taken from between thehead, or broom, and the upper most node of the broom corn stalk and issuitable in its 'entirety for the preparation of very low density fillerby theabove described process, since the relatively dense horny layerclosing the pith is very thin.

The time Nitroglycerine 13.0 15.0 Coarse NH4NO3 68 Fine NH4NOs NaNOacarbonaceous filler As illustrating the cartridge count and sensitivityof dynamites prepared according to the foregoing formulae and employingcarbonaceous filler material produced in accordance with the presentinvention as contrasted with carbonaceous filler material prepared byother methods, the following tables are given, the products pre-- paredin accordance with the present invention being indicated by an asterisk:

Formula A Sensitivity at.70 r.

y 1% Wh 1 x caro e Carbonaceous filler tridges per Half carmdgescartridges 100 pounds dynamite St St ores ores Fresh 60 days Fresh 60days Inches Inches Inches Inches Broom corn stalk, 386 ll 2 rasped.

Broom corn stalk, 445 16 i4 6 4 process of this invention.

Corn stalk, rasped- 346 13 5 Corn stalk, process 401 17 15 7 5 of thisinvention.

Flaked cereal grain 400 12 9 4 2 product.

Formula B Sensitivity at F.

No ofiy," Wh 1 x caro e Carbonaceous filler tridges per Half carmdgescartridges pounds dynamite St d St d 0T8 ore Fresh 60 days Fresh 60 daysInches Inches Inches Inches Broom corn stalk, 482 10 6 rasped.

Broom corn stalk, 540 12 11 7 6 process of this invention.

Flaked cereal grain 500 12 10 4 2 product.

A particularly important characteristic of the carbonaceous fillermaterial prepared according to the present invention and the explosivescontaining the same is the combined low density and resistance tocompression and to moisture. The latter is a particularly importantcharacteristic since the tendency for filler material heretofore,

- employed to lose bulk on exposure to moisture with consequentmushiness" of the dynamite cartridges is not encountered in explosivesprepared in accordance with the present invention.

From the foregoing description it is apparent that the present inventionaccomplishes its objects and that the explosive compositions formulatedwith carbonaceous filler materials prepared from annual plant stalks,treated in accordance with the present invention, display markedimprovements in cartridge count, sensitivity and retention ofsensitivity on storage over such explosive composition as are formulatedwith carbonaceous fillers of the prior art. Furthermore, they enable theproduction of dynamites according to Formulas A and B, havingsatisfactory sensitivity and cartridge counts over 400 and 500respectively, a result which cannot be realized with comminuted plantstalk tissue prepared by prior art methods unless they are subjected toa costly and troublesome impregnation treatment with extraneoussubstances. Due to the uniformity of particle shape and the absence ofslivers in the fillers, the mixing and cartridging of the dynamite maybe effected with unusual facility .and uniformity and the resultingcartridges are characterized by their smoothness and uniform appearance.The dynamites prepared with fillers produced by the process of thisinvention are much more resistant to the effects of moisture thancompositions formulated with the flaked cereal grain product, which issoluble in water to the extent of 35% at ordinary temperatures.

While in the foregoing description a complete disclosure of severalillustrative embodiments of the present invention has been given, it isnot to be understood that the invention is limited to variations beingpermissible in order to adapt the process to the material and producecarbonaceous fillers having optimum characteristics. It is realized thatsuch variations, modifications and applications will present themselvesto those. skilled in the art without departing from the spirit of thisinvention, and it is to be distinctlyv understood, therefore, that suchmodifications and the use of such individual features, combinations andsubcombinations of the features of the present invention as do notdepart from the spirit of this invention are, although not specificallydescribed herein, contemplated by and within the scope of the appendedclaims.

Having thus described the invention, what is claimed is:

1. A low density carbonaceous ingredient of an explosive composition,consisting of clean-cut particles of annual plant stalk, said particleshaving a density, when compressed at 12 pounds per square inch, between0.075 and 0.150 'and sorbing when saturated not more than 2.00 times itsweight of nitroglycerine.

2. An explosive composition comprising a liquid sensitizing explosive,explosive salts, and a low density carbonaceous ingredient consisting ofparticles of clean-cut broom corn stalk which being substantiallyintact, said explosive composition having a density such that a 1 Ax8inch cartridge weighs between seventy-five and ninety grams.

4. An explosive composition comprising a liquid sensitizing explosive,explosive salts, and a low density carbonaceous ingredient consisting ofclean-cut particles of corn stalk, which have a density when compressedat 12 pounds per square inch between 0.075 and 0.150, and sorb atsaturation not more than 2.00 times its weight of nitroglycerine.

5. In the art of making low density carbona- 1 ceous fillers forexplosives, the process comprising, cutting-annual plant stalks intoparticles while the stalks are moistened to their fibersaturation point.

6, In the art of making low density carbonaceous fillers for explosives,the process comprising, cutting annual plant stalks into particles whilethe stalks are moistened to their fibersaturation point, treating thecut particles with additional water, and drying.

7. In the art of making low density carbonaceous fillers for explosives,the process comprising, cutting annual plant stalks into particles whilethe stalks are moistened to their fibersaturation point, treating thecut particles with additional water, and drying at temperatures betweenand C.

8. In the art of making low density carbonaceous fillers for explosives,the process comprising, cutting broom corn stalks into particles whilethe stalks are moistened to their fiber-saturation point, treating thecut particles with additional point, treating the cut particles withadditional water, and drying at temperatures between 100 and 150 C.

11. A low density carbonaceous filler for explosive compositions,comprising clean-cut particles of broom corn stalk of a fineness such asto pass an eight mesh and be retained on a thirty mesh screen, having adensity between 0.075 and 0.150

when loaded under a pressure of twelve pounds per square inch, andcapable of sorbing not more than 2.00 times their weight ofnitroglycerin at saturation.

12. An explosive composition comprising, an

explosive liquid nitric ester having a low density carbonaceousingredient composed of clean-cut annual plant tissue having a densitywhen com-.- pressed at 12 pounds per square inch of between 0.075 and0.150, said plant tissue being capable of sorbing, at saturation, notmore than two times its weight of nitroglycerin.

EARL E. BERKLEY. GEORGE E. FROST.

